Re-evaluation of the Neuronal Centrosome as a Generator of Microtubules for Axons and Dendrites

A typical vertebrate neuron extends a single axon and multiple dendrites, both of which are rich in highly organized arrays of microtubules that serve essential functions. In simpler cell types, microtubules are organized by their attachment to a centralized nucleating structure such as the centrosome. In axons and dendrites, however, microtubules are not attached to the centrosome or any recognizable organizing structure. Over a decade ago, we proposed that the neuronal centrosome acts as a ‘‘generator’’ of microtubules for the axon and dendrites. Our studies suggested that the neuronal centrosome is highly active, especially during development, nucleating and releasing microtubules into the cell body. The released microtubules are then actively transported into the axon and dendrites by molecular motor proteins. In migrating neurons, most of the microtubules are attached to the centrosome, suggesting that significant changes in the nucleation or release of microtubules from the centrosome occur as neurons cease migration and begin to form their axonal and dendritic arbors. Recent studies suggest that the centrosome eventually becomes inactive as neurons mature, and that microtubule numbers are increased by other mechanisms, such as the severing of existing microtubules. Exactly how important the centrosome is for early stages of differentiation remains unclear, and the possibility exists that the centrosome may be re-activated in more mature neurons to meet particular challenges that may arise. Here we review historical as well as contemporary data on the neuronal centrosome, with emphasis on its potential role as a generator of microtubules. P. W. Baas (&) A. Falnikar Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, PA 19129, USA e-mail: [email protected] H. Schatten (ed.), The Centrosome, DOI: 10.1007/978-1-62703-035-9_18, Humana Press, a part of Springer Science+Business Media, LLC 2012 309